Tag Archives: Snow

Ice II (Ice-two)

Ice II (Ice two)

  • can be formed from hexagonal Ice (Ice Ih) at 198 K and 3000 bar or by decompressing Ice-five (Ice V) at 238 K
  • Ice II is likely to be a major rock-forming mineral in the outer Solar System
  • It may form a major proportion of icy moons such as Jupiter’s Ganymede
  • Density: 1.16 g/cm3

Structural features:

  • Ice-two is a proton-ordered form of ice
  • there are two types of 6-membered rings; one is almost flat (Type A) the other one has a more puckered, chair-like conformation (Type B)
  • these two types of rings are strictly alternating stacked along the c axis

  • If you look along the c axis, you will see that the two types of 6-rings are slightly rotated against each other (~ 16 degrees)

  • Space group R-3
  • Lattice parameters:
    • a = b = 12.935 Å, c = 6.233 Å
    • α = β = 90°γ = 120°

  Here, you can download the CIF.

[Atomic structure figures created with VESTA:
K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr.44, 1272-1276 (2011).]

Ice Ih

Ice Ih (Ice one hexagonal)

Structural features:

  • single molecule and molecular arrangement

  • Ice Ih is a proton-disordered phase

  • every water molecule is involved in 4 H-bonds (2 acceptors, 2 donors)
  • tetrahedrally coordinated
  • O-H bond length approx. 99 pm
  • H …. O-H distance approx. 175 pm
  • O … O distance approx. 275 pm
  • H-bond strength: approx. 21 kJ/mol
  • 6-membered rings
    • chair-like conformation in the (a,b) plane
    • boat-like conformation along the c direction

(graphic created with VESTA:
K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr.44, 1272-1276 (2011).

  • sometimes called “tridymite ice” because the oxygen atoms occupy the Si analogeous positions in the SiO2 phase tridymite
  • Space group P63/mmc
    • a = b = 4.4975 Å, c = 7.3224 Å
    • α = β = 90°, γ = 120°

 Here, you can download the CIF.